Intermodal cargo containers (also referred to as dry cargo containers, freight or shipping containers) are reusable transport and storage units for moving products and raw materials between locations, including between countries. Intermodal cargo containers are standardized to facilitate intermodal transport such as among marine transport, freight train transport, and freight truck transport.
Containerization has provided global commerce with many benefits. Shipped goods move more easily and cheaply. Manufacturers know that goods loaded at one location can be readily unloaded at the destination. Cargo security has been improved, as containers are usually sealed and can be locked to discourage tampering and theft. Containers also have a longer service life, and there is a stronger market for used containers. Additionally, the costs of cargo containers themselves are lowered because a manufacturer can make these in larger volume knowing that potential customers are available all over the world.
Several international standards have been created to promote international containerization. For instance, the International Organization for Standardization (ISO) has promulgated applicable standards including R-668 to define terminology, dimensions, and ratings; R-790 to define identification markings; R-1161 to recommend corner fittings; and R-1897 to set forth dimensions for general purpose containers. Other standards include ASTM D5728-00, ISO 9897 (1997); ISO 14829 (2002); ISO 17363 (2007); ISO/PAS 17712 (2006); ISO 18185 (2007); and ISO/TS 10891 (2009). An international specification for coating/paint performance is provided by Institute of International Container Lessors (IICL). See also International Organization for Standardization (ISO), Freight Containers, Vol. 34 of ISO Standards Handbook, 4th Ed., 2006, ISBN 92-67-10426-8; and Levinson, Marc, The Box: How the Shipping Container Made the World Smaller and the World Economy Bigger, Princeton, N.J., Princeton University Press, 2006, ISBN 0691123241. Each of these standards and publications, and all other publications referenced herein, is incorporated herein in their entirety for all purposes.
Intermodal cargo containers are typically assembled by welding together a number of individual metal components. To prevent corrosion during welding, the components are cleaned (for example, by shot-blasting) and then coated with primer compositions that provide temporary corrosion protection. Such compositions are known as shop primers and allow primed components to be welded through the primer layer without having to remove the primer coating near the weld. After welding and assembly, the primer coating near the weld may be removed to allow inspection of the welded area. The inspected area may be over-coated with a primer and optionally, a topcoat to provide extended corrosion protection and the desired aesthetic appearance.
Welding is typically performed using automated welding equipment, especially where repetitive assembly steps are common. Automatic welding equipment is, however, prone to malfunction when the surface to be welded is non-uniform. This leads to defects or holes burned through the metal during welding, or localized failure to form welds.
Conventional shop primers are solvent-based epoxy compositions. Water-based systems have been unable to satisfy the applicable performance demands and/or standards. Consequently, only solvent-based coating systems have found widespread commercial acceptance in the industry. The container industry retains a strong bias against using prior proposed water-based coating systems.
With increased environmental awareness, there is a strong desire to develop improved technology that would allow use of water-based coating systems as shop primers. Significant challenges remain. As one serious challenge, it has been very difficult to formulate water-based shop primers that show acceptable adhesion and corrosion resistance while also being weldable.
From the foregoing, it will be appreciated that what is needed in the art is a coating system for use as a shop primer that is water-based and provides optimal corrosion resistance and weldability.